Seed dispersal of Diospyros virginiana in the past and the present: Evidence for a generalist evolutionary strategy

Abstract

Several North American trees are hypothesized to have lost their co‐evolved seed disperser during the late‐Pleistocene extinction and are therefore considered anachronistic. We tested this hypothesis for the American persimmon (Diospyros virginiana) by studying the effects of gut passage of proposed seed dispersers on seedling survival and growth, natural fruiting characteristics, and modern animal consumption patterns. We tested gut passage effects on persimmon seeds using three native living species, the raccoon (Procyon lotor), Virginia opossum (Didelphis virginiana), and coyote (Canis latrans), and two Pleistocene analogs; the Asian elephant (Elephas maximus) and alpaca (Vicugna pacos). Persimmon seeds excreted by raccoons, coyotes, and elephants survived gut transit. Gut passage did not affect sprouting success, but did tend to decrease time to sprout and increase seedling quality. Under field conditions, persimmon fruits were palatable on the parent tree and on the ground for an equal duration, but most fruits were consumed on the ground. Seven vertebrate species fed upon persimmon fruits, with the white‐tailed deer (Odocoileus virginianus)—a species not capable of dispersing persimmon seeds—comprising over 90% of detections. Conversely, potential living seed dispersers were rarely detected. Our results suggest the American persimmon evolved to attract a variety of seed dispersers and thus is not anachronistic. However, human‐induced changes in mammal communities could be affecting successful seed dispersal. We argue that changes in the relative abundance of mammals during the Anthropocene may be modifying seed dispersal patterns, leading to potential changes in forest community composition.

Multiple External Seed Dispersers Challenge the Megafaunal Syndrome Anachronism and the Surrogate Ecological Function of Livestock

“…Therefore, the results of this study suggest that fruits of these palms cannot be further supported as anachronistic. These findings add to growing evidence indicating that assumptions related to extinct megafauna because of their large size are not necessary to understand all past and current mutualistic frugivore-large fruit interactions (Howe, 1985;Jansen et al, 2012;Baños-Villalba et al, 2017;Rebein et al, 2017;Carpenter et al, 2018).…”

“…Overall, external dispersal emerges as the major mechanism exploited by these large-fruited plants to disseminate their seeds at variable distances by an array of dispersers. Information on disperser assemblages of the study palms in other geographical areas (Zona and Henderson, 1989;Eiserhardt et al, 2011;Virapongse et al, 2017), as well as on other large-fruited plants (Jansen et al, 2012;Tella et al, 2015Tella et al, , 2019Blanco et al, 2016;Rebein et al, 2017) support these mixed redundant and complementary dispersal systems by ectozoochory. Indeed, studies revisiting and adopting the megafaunal seed dispersal hypothesis recognized guilds of external dispersers with a role in population dynamics of these plants, although overlooked their potential impacts as selective agents shaping large size and other fruit traits (Guimarães et al, 2008;McConkey et al, 2018).…”

“…This study negates the idea that overbuilt, fleshy fruits of the study palms are today maladapted for dispersal by contemporary fauna. Since the work of Janzen and Martin (1982), evidence has been building in support of seed dispersal of putative anachronistic plants by contemporary fauna (e.g., Jansen et al, 2012;Baños-Villalba et al, 2017;Rebein et al, 2017;McConkey et al, 2018), whose members existed in the same or much earlier geological periods as the extinct Pleistocene megafauna (Koch and Barnosky, 2006;Wright et al, 2008;Eriksson, 2016). Therefore, efforts are encouraged to rethink whether fruits assumed to have adjusted to a "megafaunal syndrome" actually required the past participation of extinct megafauna and to consider the contemporary function of domestic surrogates for seed dispersal.…”

“…A comparative study of Neotropical large-fruited plants revisited and refined the megafaunal seed dispersal hypothesis, introducing an operational definition and classification of megafaunal fruits, like oversized fruits with fleshy pulp packaging extremely large individual seeds or large numbers of moderatelysized seeds (Guimarães et al, 2008). In using these criteria, subsequent studies have adopted the conjecture that extinct megafauna acted as legitimate past dispersers of many oversized fruits (Onstein et al, 2018;van Zonneveld et al, 2018), while others critically tested its assumptions given knowledge on the effectiveness of smaller contemporary dispersal agents using variable dispersal mechanisms (Jansen et al, 2012;Boone et al, 2015;Baños-Villalba et al, 2017;Rebein et al, 2017;Carpenter et al, 2018;McConkey et al, 2018). Multiple variably-sized extant dispersers and abiotic factors have been recognized in present-day dispersal interactions with "megafaunal plants, " while assuming the existence of body-size trade-offs constraining dispersal ability via fruit ingestion and seed defecation (Donatti et al, 2007;Guimarães et al, 2008;Pires et al, 2018).…”

Seed dispersal potential of jackals and foxes in semi-arid habitats of South Africa

“…Additionally, germination of seeds in canid scats has been investigated in several previous studies. In general, the pulp removal and seed scarification that occurs when canids consume fruit has been shown to improve germination rates or increase seedling quality over non-consumed seeds (Juan et al, 2006;Varela and Bucher, 2006;Cazetta and Galetti, 2009;Rosalino et al, 2010;Rebein et al, 2017;Escribano-Avila, 2019) although results can vary depending on the fruit species (Cypher and Cypher, 1999). And in contrast to ungulates (Bodmer, 1991), seeds consumed by canids are generally defecated whole, because very few are destroyed during mastication and digestion (Herrera, 1989;Chavez-Ramirez and Slack, 1993).…”